In this issue:
THE BACK ANGLE
RAMPING THE STRING HOLES
CHECKING THE FRETBOARD SLOPE

Hello! again, to all you dedicated guitar lovers who want to know how the guitar
does what it does and how it can be made to do it better. In this issue, you will find a
continuation of my greater plan to address the whys and hows of neck resets.

If you haven't already noticed, you will at the end of this issue have discovered
my devious master plan: by the time we finally get down to whether and how a neck reset
should be done, you will all have been carried (without hardly noticing it) across the
entire panorama of ideal vs. real-world guitar design, setup and construction.

In Newsletter #2 we had learned how to lower the saddle precisely, resulting in a
desired action height. But we were dealing then in an ideal world of guitars with good
neck angles. Alas, the real world rushes in: your Taylor, Guild, Martin--or Gurian-- may
have little or no saddle left to cut down. And your action is still high and
uncomfortable. Ah, tension, like rust, never sleeps.

What are, however, the consequences of lowering the saddle? Just that the action
drops? No, like so many other things in life, there's a price to pay: you in fact reduce
the instrument's power output and affect it's "feel" by a certain amount. If you
have good auditory memory, by a noticeable amount. But why, you may ask?

THE BACK ANGLE

When we raise or lower the saddle, we steepen or flatten the "back
angle."-- the angle the strings drop from the crown of the saddle and into the string
holes. We luthiers worry about those few degrees of back angle. Because when we change the
saddle's height we consequentially affect the way the strings dump their tension onto the
guitar.

We could say that the strings, when vibrating, are tapping a kind of sonic Morse
Code on the saddle. If we did, we would be partially right: yes, it is indeed sublimely
ordered information which emanates from the oscillating string. But the information is far
more concentrated than dit-dit and dah. True, the string's movements result in a sequence
of tiny tugging and releasing motions, what results as the string travels to the limit of
its envelope (pulling oh-so-minutely on the saddle), and back to its at-rest location
(lessening for an instant its pull on the saddle). Then, its own momentum carries it
beyond that, to the opposite extreme of its envelope (pulling the saddle again). As it
strains against the string's own elasticity, the string whips back in the opposite
direction again, and so on. The saddle is receiving all this "code" and levers
it onto the top of the guitar.

But all this is not just happening in just in an up-and-down or side-to-side
plane: it is happening in all directions; towards the nut, away from it, up, down,
sideways, and in a virtually infinite number of discrete rotations. This is how the string
couples the sum of all its myriad harmonic motions to the guitar.

The sum total of the string's effect on the saddle, and because it is immobiled
into the bridge, on the soundboard, is to induce it into rocking, swaying, jumping,
tipping, heaving, rotating--like an airplane in a storm---restrained only by the
soundboard's limiting resilience.

I like to picture in my mind what the surface of the soundboard must look like
while you play the guitar, as if you were as big as a microbe. Undoubtably it is
physically deflected in all planes, and it is further deflected due to motions and forces
"feeding back" onto it -- energy being returned BACK to the bridge and then to
the strings themselves. The soundboard feeds back the ordered kinetic energy imparted to
it by the strings, returning it from the driven sides, back and the air mass partially
trapped in the soundbox, all resonating back in turn. Add to the mix the myriad of motions
wich the opposite end of the strings are feeding into the neck. Again, in turn, that
energy eventually is returned to the box, but altered in its own peculiar way.

What we are dealing with is what the acousticians call a set of "linked
oscillators:" springs attached to springs attached to springs attached to springs.
And then the spring ends are attached to each other. The string is a spring, the thin
soundboard--limited by its resilient braces, is a spring restrained by springs; the air
partially trapped inside the soundbox is another spring. The neck shaft is whipping around
like crazy, itself a big massive spring.

The largest, simplest motions, occurring at lower frequencies are the easiest to
discern and to understand. Acousticians have identified and can even visually demonstrate
their movements. But the rest--there are simply so many and they overlap so closely--are
only partially fathomable by the application of statistical analysis.

My mental model of the guitar's soundboard while one is playing, is a flexible
membranic surface which appears like the surface of the water in a pan heated to a rolling
boil.

But I digress...

The amount and quality of the string's influence over the saddle and bridge is
determined directly by the string's back angle. That is, again, the angle at which the
string drops BEHIND the saddle and into the bridge. The back angle is changed by two
things: the height of the saddle above the bridge, and the distance of the saddle to the
string holes.

So yes, we reduce the back angle when we cut down the saddle and, correspondingly,
the string's effect on the soundboard. We could analogize the system to somebody with a
crowbar. The string's motive force is the guy yanking on the crowbar. The saddle/bridge
height over the soundboard is the length of the long arm of the crowbar. As we drop the
saddle, we shorten the arm of the long arm of the crowbar, reducing its mechanical
advantage over the soundboard.

And the back angle? I can wring the last bit of juice from this crowbar analogy by
likening the back angle to two factors on the crowbar: as we lower the saddle, we loosen
the guy's grip on the crowbar--from a two-fisted grip when the saddle is at full height
over the bridge, to a simple thumb-and-forefinger grip when the saddle is a merely a
protruding sliver. As the entry-holes in the bridge get closer to the saddle, we shorten
the SHORT arm of the crowbar, similarly increasing its power, just like lengthening the
long arm did.

I promise, this is the last stretch of this tired analogy. What happens if the
saddle is very, very tall, and the strings holes are socked up real close to the towering
saddle? Well, in this extreme case (and believe me, I've seen more than a few student
guitars like this) the exposed part of the saddle starts to bend. The front lip of the
bridge threatens to tear off and, as well, the bottom belly of the bridge wants to start
peeling off the soundboard (but if it's stuck on there real good, the soundboard and all
the braces will want to start bending or peeling off, instead). It's not pretty. But boy,
it's going to be a LOUD, raucous-sounding guitar while it holds together!

If you've had to drop the saddle radically when setting the action to a more
comfortable level, chances are you will have reduced the string's back angle so much that
there now will be insufficient pressure on the saddle. The result is often an annoying
whine when playing all the notes on that string, or at least a distinctive wimpy, wowing
sound.

RAMPING THE STRING HOLES

One remedy to this problem that occurs when you cut down the saddle excessively,
(recommendable only if you're cheap, or the guitar is cheap, or if the guitar is badly
beat up anyway, or if you're not fussy) is to "hot rod" the bridge by
"ramping," or extending the little string-notches in the string holes, so that
the string now enters the bridge top sooner. This can restore some of the "lost"
back angle, increase the string's down-pressure on the saddle and eliminate the wimpy
whine.

Alternatively, judicious shaving of material from the bridge top also can restore
the back-angle. Indeed, you may actually improve the function of the bridge by contouring
its surface to better match the contour of the fretboard. The payoff is that more of the
saddle is exposed, and the back angle can thus be restored. That's what the builder should
have done in the first place. However, shaving the bridge on an expensive, name guitar is
usually bad practice -- unless the bridge is too thick to begin with. They do come through
that way sometimes, you know. I know Martin use to make bridges available of varying
thickness for the bridger to chose from, to best suit the neck angle of the guitar at
hand. So you can expect to see original bridges on Martin guitars of the same model and
vintage varying from about ¼-inch to a full 3/8-inch. Any bridge over 5/16-inch in
thickness is a potential candidate for re-countouring.

One thing: have you noticed that even though the steel-string saddle is angled,
the common line through the centers of the bridge holes isn't? The result (which I believe
is inadvertent and unplanned) is that the treble strings, whose bridge-holes are further
from the saddle than with the bass strings, will have a flatter back angle and the bass
strings will have a steeper angle. This can't be a good thing. It can only exacerbate the
weakening of the treble response when the saddle must (invariably) be cut down later. For
another thing it can only hobble the instrument's treble-string response under all
circumstances.

I, for one, now determine the bridge-hole centerline to be strictly parallel to
the slanted saddle. Visually, nobody has even noticed it or even commented. But it can't
help but give the treble response more snap than on the traditional design. And, as the
curmudgeonly builder and textbook author Arthur Overholtzer once said, "I don't mind
tradition, as long as it doesn't interfere with some of my ideas."

--------

If you haven't guessed by now, I'm subtly telling you all the ways to avoid or put
off the inevitable neck reset. But is there some kind of measurement that can tell you, at
a glance, just how "off" the neck is? Well, certainly, if your action is still
high after you've done all the above, it will only come down with a neck reset. But here
is another test:

CHECKING THE FRETBOARD SLOPE

To check whether a guitar's fretboard has correct inclination (and by extension,
the neck angle is correct) first remove the instrument's strings. Adjust the truss rod to
allow the fretboard to read the neck as straight as possible against a straightedge place
along the centerline of the neck (keep it well aligned, now. If it crosses the centerline
at a slight slant, it will inevitably read a hump in the middle). The straightedge may
rock over a single high or loose fret. (Tap or file down the offending fret, or repair it
with a dot of cyanoacrylate).

Notice if the straightedge is lifted off the frets by the fingerboard-end rising
slightly. Often it will. In mild cases, tightening the truss rod nut will average out the
problem. However, if the end of the fingerboard rises in the extreme, you might as well
stop the test right now. This is usually a tell-tale sign of a bad neck angle. But this is
the extreme case. We're talking about mild, borderline cases: the kind that require fine
judgement calls.

With the straightedge thus placed on the frets, its far end should just
"tickle" the top of the bridge on a well settled-in, well-used guitar. On a
brand-new guitar that has yet to settle in (or on a 12-string guitar, which is expected to
always settle considerably under tension) the straightedge should clear the bridge by not
over 1/16-inch (1.5mm). There is an exception: on new 6- and 12-string guitars which are
intended to carry medium gauge strings exclusively, the straightedge should clear the
bridge by 3/32" (2.5 mm). On a classic guitar, the straightedge should not clear the
bridge, but rather should touch the front of the bridge about 1/16-inch BELOW the top edge
of the front lip, since lower tension and higher average actions are the norm on
classicals.

Usually on a guitar with a workable, rather than ideal neck angle, the
straightedge will just bump into the bridge a hair below the top edge. In that case
(following the guidelines indicated above) a gentle recountouring of the bridge will make
everything shine--on the cheap.

But many guitars fail this neck-angle test. Unfortunately, a good neck angle is a
rare thing, indeed -- even, alas, on many brand-new guitars hanging in the average music
store.

I recently visited a major guitar factory to assist a good friend in selecting a
guitar (he was an ace dealer and his reward was to pick one out). Only one guitar in a
dozen had anything even approaching an ideal neck angle. He couldn't believe it. The guys
in the factory got most upset at me. I felt like the messenger with bad news that was
about to be killed. Most of the guitars we examined (which, indeed, were ready for
shipping), had string actions higher than would be comfortable for the ordinary player,
and saddles which invariably were too low.

When a new guitar like that reaches its destination and its already-low saddle is
adjusted (by the music store techie) down even further in order to remedy the stiff
action, there will be nothing left to adjust over the guitar's long future of progressive
settling-in. Virtually all the guitars we examined in the shipping room of that guitar
factory were candidates for an expensive neck reset barely five or six months down the
road -- if not right then and there. After examining about fifty guitars, we found one
that happened to have nice low action, and a full-height saddle. I don't want to go
through that ordeal again.

Ideally, after a guitar receives its first readjustment following an initial
settling-in period, there ought to be sufficient saddle height left for a long lifetime of
downwards adjustments. On all these guitars, a better neck angle would have assured this
"quality." Sadly, the production engineers at that factory missed a golden
opportunity to impart this additional measure of value into their instruments.

NEXT TIME:

NECK ANGLE AS A MEASURE OF INSTRUMENT QUALITY
THE EFFECT OF SCALE LENGTH ON THE INSTRUMENT'S RESPONSE
And more...